// Copyright 2014 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef UI_EVENTS_GESTURES_FLING_CURVE_H_
#define UI_EVENTS_GESTURES_FLING_CURVE_H_

#include "base/macros.h"
#include "base/time/time.h"
#include "ui/events/events_base_export.h"
#include "ui/events/gesture_curve.h"
#include "ui/gfx/geometry/point_f.h"
#include "ui/gfx/geometry/vector2d_f.h"

namespace ui {

// FlingCurve can be used to scroll a UI element suitable for touch screen-based
// flings.
class EVENTS_BASE_EXPORT FlingCurve : public GestureCurve {
public:
    FlingCurve(const gfx::Vector2dF& velocity, base::TimeTicks start_timestamp);
    ~FlingCurve() override;

    // GestureCurve implementation.
    bool ComputeScrollOffset(base::TimeTicks time,
        gfx::Vector2dF* offset,
        gfx::Vector2dF* velocity) override;

    // In contrast to |ComputeScrollOffset()|, this method is stateful and
    // returns the *change* in scroll offset between successive calls.
    // Returns true as long as the curve is still active and requires additional
    // animation ticks.
    bool ComputeScrollDeltaAtTime(base::TimeTicks current, gfx::Vector2dF* delta);

private:
    const float curve_duration_;
    const base::TimeTicks start_timestamp_;

    gfx::Vector2dF displacement_ratio_;
    gfx::Vector2dF cumulative_scroll_;
    base::TimeTicks previous_timestamp_;
    float time_offset_;
    float position_offset_;

    DISALLOW_COPY_AND_ASSIGN(FlingCurve);
};

} // namespace ui

#endif // UI_EVENTS_GESTURES_FLING_CURVE_H_
